In addition to the purchase of UWW, was also that of a normal zoom lens for me. Since I own a EOS 450D as a body, in this case the crop factor had to be taken into account to a focal length of about 16 in the downward direction - 17mm still have a good wide angle. After some research, it seemed to me the Tamron 17-50 f / 2.8 with its very good test results, and a great value for money as most suitable for my purposes. I bought it on Amazon, ultimately, there was, however, already within one month back (return went the way without any problems). What I disliked was Tamron especially that of AF apparently did not sit properly and resulted in relatively blurred photos. In addition, my colors and contrasts appeared somehow artificially; as a benchmark served me the pictures with the Canon kit lens (18-55 f / 3.5 to 5.6 IS) that looked much more natural. I decided now to want to make any more compromises and for the EF-S 17-55 f / 2.8. Tests and reviews more owners in various Internet forums attested the Canon excellence especially in the Focus already in full aperture range. Problems there should be only with the tube and chromatic aberrations Staubeinlässen. The former would, however, not really affect the imaging performance and the latter was quickly corrected with graphics programs. Meanwhile, I have the Canon since November 2008 and am happy with him around (dust problems, there is so far no). Above all, the IS pleased me repeatedly as good pictures even in quite dark and fair, despite a longer exposure time are possible. I am also delighted with sharpness and colors and contrasts.
Conclusion: I would recommend the EF-S 17-55 f / 2.8 buy repeatedly.